Self-wound facestock has an adhesive-coated back surface; but instead of using a separate release liner to protect the adhesive coating prior to use, a release coat is applied to a front surface of the facestock. The release coat on the front surface of one coil of a roll contacts the adhesive on the back surface of an adjacent coil of the roll. Elimination of the liner saves costs and increases the length of the facestock in a given diameter roll.
Most release-coated surfaces have low adherence not only to adhesives but also to many inks as well. Accordingly, significant modifications are required to print on such release coats. For example, U.S. Pat. No. 4,708,907 suggests the addition of fine particles of inorganic filler such as talc, silica, and calcium carbonate to make release-coated surfaces more writable.
Direct thermal printable facestock is readily printable through release coat. In fact, the release coats have been found to enhance the transfer of heat between thermal print heads and underlying direct thermal printable layers. For example, Japanese Application No. 59-107264 discloses a self-wound facestock in which a release agent is applied to a direct thermal printable layer on one surface of a substrate and an adhesive layer is applied to the opposite surface of the substrate.
Dust and debris tend to accumulate on thermal print heads, especially when paper substrates are used, requiring periodic cleaning to maintain image quality. Generally, the print heads are manually cleaned after completion of a roll of facestock. Self-wound rolls of direct thermal facestock may extend the roll length by as much as sixty percent when compared to a lined facestock of the same diameter, so it is important to defer cleaning the print heads for an even longer duration. However, we have found that thermal print heads foul more quickly when printing through release-coated surfaces, possibly because the release-coated surfaces are not sufficiently porous or abrasive to transport debris past the print heads.